At the top of a small hill in suburban southern California, there is what appears to be a thicket of stunted, gnarled oak trees wedged between a pile of boulders. A passerby would likely miss this ancient, biological wonder.
The entire grove of trunks is in fact one plant, a newly discovered Palmer's oak (Quercus palmeri) that researchers estimate is over 13,000 years old, making it one of the oldest plants on Earth.
Researchers, led by Michael May of the University of California, Davis, found the tree a decade ago during a routine survey of local plant life.
It's easy to miss; none of its 70 stems get more than a few feet tall, and it grows in a boulder pile that doubles as shelter from the area's buffeting winds.
At first glance, the scientists thought it was an isolated grove of trees, but something didn't add up: None of them produced fertile acorns, so the plants couldn't reproduce.
The trees were a little too similar in appearance, too — almost like identical twins. And Palmer's oaks typically don't grow in the hot, parched environs of Riverside County.
The team began to suspect they were looking at a clone.
Genetic analysis confirmed their suspicion. Each of the 70 stems are genetically identical; they are the same plant, currently growing in an oval 25 yards long and 8 yards wide.
Plants can clone themselves in a number of ways. Aspen, for example, sprout roots that grow into new stems, allowing these plants to spread several feet each year.
Scientists estimate an Aspen stand in Utah, called Pando, may be tens of thousands of years old, though estimates vary widely. And a creosote bush growing in the Mojave Desert — dubbed King Clone — has been reliably dated at nearly 12,000 years old using carbon isotopes.
"Getting a handle on how old these organisms are is hard; most estimates are based on growth rates," which can have large errors, team member Jeffrey Ross-Ibarra also of the University of California, Davis said.
The team estimated that the newly discovered oak, which they named the Jurupa Oak after the mountains in which it grows, started from a central trunk and grew outward at a rate of one-twentieth of an inch each year, relying on fire to burn down stems and trigger the plant to send out new sprouts. The team's findings are reported in the online journal PLoS One.
But any trace of ancient wood has been lost to termites, so they team is left with a guess. It could be anywhere from 5,000 to 30,000 years old, Ross-Ibarra said, dating to a time when the Jurupa Mountains were cooler and wetter, and Palmer's oaks were prevalent.
"If they're right about how the oak regenerates, then their age estimate seems valid and true," Jennifer DeWoody of the University of Southampton in the United Kingdom said. "This could be a very old tree."
Today the tree's closest neighbors are a housing development, invasive grasses and a nearby limestone quarry. And while it has proven its ability to weather natural climate change, Ross-Ibarra fears the Jurupa Oak's future is in jeopardy at the hands of the developer's bulldozer.
"I'm cynical about its chances over the next hundred years," he said.